In the related art, there is known a heat treatment apparatus in which a duct is installed outside a reaction tube and gas injection holes for bringing the interior of the duct and the interior of the reaction tube into communication with each other are formed in an outer wall of the reaction tube so that a gas is supplied from the duct into the reaction tube through the gas injection holes. With this configuration, it is not necessary to install an injector for supplying a gas between an inner wall of the reaction tube and substrates. This makes it possible to reduce a clearance between the inner wall of the reaction tube and the substrates. In this heat treatment apparatus, the interior of the reaction tube is vacuum-exhausted during a heat treatment and the outside of the reaction tube is kept at an atmospheric pressure level. Thus, a high pressure is applied to the outside of the duct communicating with the interior of the reaction tube which is a vacuum region. Accordingly, the duct needs to be a structure having a pressure resistance property.
Furthermore, as a substrate processing apparatus having a similar structure, there is known a substrate processing apparatus in which a plurality of injection holes is formed in an outer wall of a substantially cylindrical process chamber and a tube is installed so as to surround the vicinity of a central region of the process chamber in a longitudinal direction. A cylindrical space sandwiched by the process chamber and the tube is used as a gas introduction space. A gas introduced into the process chamber is heated in advance within the gas introduction space having a large surface area. In this substrate processing apparatus, a partition plate extending in a vertical direction is installed within the gas introduction space and a zigzag-like flow path extending up and down is formed.
However, in the conventional heat treatment apparatus, the gas is supplied to the duct as a flow orientated from a bottom portion of the reaction tube toward a top portion thereof. Thus, the supplied gas in the bottom portion of the reaction tube is not sufficiently pyrolized although the supplied gas in the top portion of the reaction tube is sufficiently pyrolized. As a result, the heat treatment of the substrates disposed in the bottom portion of the reaction tube is less sufficient than the heat treatment of the substrates disposed in the top portion of the reaction tube. Thus, there may be a case where a difference in treatment amount occurs between the substrates disposed in the top portion of the reaction tube and the substrates disposed in the bottom portion of the reaction tube.
Furthermore, in the conventional substrate processing apparatus, the gas introduction space is formed in the vicinity of the middle portion of the reaction tube in a height direction. However, in a vertical substrate processing apparatus, a region existing near the top portion of the reaction tube is a region where a temperature is easy to rise. Thus, there is a problem in that the efficiency of pyrolysis is not so high. In addition, the flow path is formed by the partition late within the tube. This poses a problem in that it is difficult to freely form the flow path.